Date of Award

Spring 2004

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean/Earth/Atmos Sciences

Program/Concentration

Oceanography

Committee Director

Glenn Cota

Committee Member

Larry P. Atkinson

Committee Member

Zhonghai Jin

Abstract

Bio-optical observations were made during August 2000 in the Beaufort and Chukchi Seas. Chlorophyll a concentration (Chl) ranged from 0.068 to 18.51 mg chl m−3. Both total particulate and phytoplankton absorption at 443 nm were closely correlated with chlorophyll concentration. There is no strong correlation between chlorophyll concentration and absorption by soluble materials or nonpigmented particulates. Absorption, scattering, and attenuation all show strong first-order spectral relationships. Two semianalytical remote sensing reflectance models were evaluated and validated using bio-optical data collected in this region. Both models were proficient at retrieving chlorophyll concentration, phytoplankton absorption coefficients, and particulate backscattering coefficients. A chlorophyll-dependent reflectance model was also assessed, and proved to be highly successful in reproducing measured reflectance spectra. A four-component, Case 2 model with mean absorption spectra for phytoplankton, soluble materials, and nonpigmented particulates was employed in HYDROLIGHT simulations. The remote sensing reflectance spectra simulated in the radiative transfer model were in excellent agreement with field data. Regionally tuned algorithms explained >93% of the variability in the surface chlorophyll concentration. Time-series of remotely sensed distributions of sea ice, surface temperature, albedo, clouds, and phytoplankton were examined to evaluate variability of environmental conditions and physical forcing of phytoplankton in the Beaufort and Chukchi Seas. Large-scale distributions of these parameters were studied for the first time using weekly and monthly composites from April 1998 through September 2002. Seasonal variations of ice cover dominated environmental conditions, and ice edge blooms followed retreating marginal ice zones northward. Blooms were most prominent in the southwestern Chukchi Sea, and were especially persistent immediately north of the Bering Strait in nutrient-rich Anadyr water and in some fronts. Chlorophyll concentrations increased from April to reach a maximum value in spring or summer depending on location. Large interannual variability of ice cover and phytoplankton distributions were observed. Phytoplankton responded rapidly to environmental changes with increases in biomass to large accumulations during 1998 in the Beaufort Sea when sea ice retreated early. Annual variations of mean surface temperature were also evident with 1998 being the warmest year. Correlation analyses between chlorophyll and a single environmental parameter showed relatively high negative correlation with ice concentration but a positive correlation with surface temperature.

DOI

10.25777/01jr-f671

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